The present invention relates to signs and more particularly to signs or guidance markings which indicate an exit or path of egress from a public building or conveyance (generally, an “exit sign”).
Building codes, transportation safety codes, and other regulations require exit signs to be very easy to see. Typically, five foot-candles of light are required on the face of an exit sign all the time a building is occupied. To meet this requirement, battery backup systems have been employed to keep signs illuminated during power failures. However, battery backup systems have several limitations. They require periodic bulb/tube replacement, battery replacement and testing. They consume power all of the time. The battery charger and other electrical components are subject to failure and replacement. The inoperability of the battery backup system is likely to go unnoticed until a scheduled test date or a power failure. In the latter case, lives may be endangered.
The present inventors also believe there is a need for relatively compact exit signs designed to be mounted close to the floors of buildings and conveyances so that people moving below a layer of smoke can find their way out. Thin profile signs are particularly well suited for this purpose because they are less likely to impede traffic or to cause or sustain damage than exit signs designed to be installed above a door frame, where the sign's depth was relatively immaterial.
Improvements in photo-luminescent materials have led to signs that are bright enough to stand alone and pass Underwriters Laboratories® requirements. U.S. Pat. No. 6,364,498 discloses a sign that uses a powered light source to illuminate the lettering or other characters and to energize photo-luminescent pigment during normal operation. The pigment glows and thereby illuminates the lettering in the event of a power failure. It is believed that the drawbacks to this prior art photo-luminescent sign were its relative bulkiness and relatively substantial energy and maintenance requirements.
Thus the present inventors were faced with the problems of developing an exit sign that (1) does not need a secondary or emergency source of electricity to meet illumination requirements; (2) requires less electrical power and maintenance than prior art exit signs; and (3) can be produced with a thin profile to meet floor or low wall mounting requirements.